This invention relates to a novel grease thickening agent. More particularly, this invention concerns a novel metal-containing polyurea thickening agent.
Modern technology is currently supplying the general public and the process industries with machinery which is designed to operate under a wider range of temperatures and under greater loads than previously available. In addition, most of the newer machines are designed to operate at extremely high speeds. Many of these machines require certain specific lubricating properties which are not available in the conventional lubricants. Thus, modernization of high speed and high temperature equipment has strained the petroleum industry for the development of a second generation of lubricants capable of satisfying the requirements of the new machines. Recently, for example, there has been an increased demand for grease lubricants capable of performing well at temperatures above 300.degree. F. in high speed bearings and gears for periods in excess of 500 hours. In addition, with the further development of the high speed sealed bearings, the grease must be able to endure for the life of the bearing.
There have been numerous grease compositions developed which satisfy most of the new more stringent requirements. Many of these compositions, however, are entirely too expensive for commercialization or only meet some of the lubricating requirements and fail in others. One type of lubricant currently available is the ubiquitous lithium greases. These greases are simply a mixture of a hydrocarbon base oil and a lithium hydroxy stearate thickener with minor amounts of other additives. Although these greases exhibit good lubricating properties and perform well at moderate temperatures, its application in high temperture and high speed machinery has not been entirely successful. The lithium greases tend to deteriorate in these machines at high temperatures, particularly at temperatures above 300.degree. F. The deterioration leads to a rapid loss of lubrication and ultimately failure of the equipment.
Another type of grease composition which has excellent lubricating properties at the higher temperatures is comprised of a lubricating oil (natural or synthetic) containing a polyurea thickener. This type of lubricant is disclosed in U.S. Pat. Nos. 3,242,210; 3,243,372; 3,281,361; 3,284,357; 3,346,497; and 3,401,027, all assigned to the Chevron Research Company. The polyurea thickener imparts a significant high temperature stability to the grease and, in fact, effects a mild anti-thixotropic property, i.e., increase in viscosity with increasing shear, to the lubricant. This property of the lubricant is advantageous to prevent the segregation or loss of grease from the moving parts of the machine. While the polyurea grease has solved most of the problems associated with the older lubricants, a need still exists for an improved thickener which, when incorporated into a grease composition, can be used for longer periods at elevated temperatures; and, yet, still be relatively inexpensive to make.
It is, therefore, an object of this invention to provide a new thickening agent.
It is another object of this invention to provide an improved grease thickener capable of imparting good lubricating properties to a grease at high temperatures over prolonged periods.
It is another object of this invention to provide a relatively inexpensive grease thickening agent capable of performing well at high temperatures in high speed application.
It is another object of this invention to provide a method of making an improved grease thickening agent.